In an existing LTE (Long Term Evolution) system, an eNB (evolved NodeB) may estimate channel quality of an uplink channel based on an SRS (sounding reference symbol), to perform uplink scheduling based on the channel quality estimated by the eNB, or may obtain channel quality of a downlink channel based on the SRS by using channel reciprocity, to implement downlink scheduling and transmission. A current standard has two different types of SRSs: a periodic SRS and an aperiodic SRS.
With rapid development of a mobile service, supporting an LTE system in accessing an unlicensed spectrum is an effective manner to improve service quality of the mobile service. In addition, an LAA (licensed-assisted access, or unlicensed spectrum) system is introduced into the 3GPP (3rd Generation Partnership Project). The LAA system accesses the unlicensed spectrum by using a CA (carrier aggregation) technology and a licensed-assisted access using LTE system.
In the prior art, when sending an aperiodic SRS, a terminal device can send aperiodic SRSs on only some fixed symbols in a subframe. If the fixed symbols in a subframe are used to send downlink data or send other uplink data, the existing terminal device cannot send the aperiodic SRS. In the LAA system, a problem that the existing terminal device cannot send the aperiodic SRS is particularly serious.